Renault E-TECH: Developing an advanced hybrid system from Lego concept

The LEGO model all was the at the fore of the development of Renault’s advanced E-TECH powertrains. Transforming the toy prototype into a real, working engine was the next step which that faced Ahmed Ketfi-Cherif, Renault’s Mechatronics Synthesis Architect.

Designer of the initial LEGO prototype Nicolas Fremau, consulted Ahmed to bring the E-TECH hybrid powertrain to life as well as Renault’s wider hybrid plans. He said “Going from the LEGO adventure to reality was a massive challenge. It taught me a lot.”

Smooth operation was a priority

As a control specialist, Ahmed needed to ensure that transitions between each driving mode were possible with a simple ‘dog clutch’ which is normally associated with motorsport. It was also paramount that the finished product would be up to the high standard demanded by the customer.

The dog clutch system that replaces both a sprocket and synchronising ring in a clutchless configuration is a gearbox boasting superior efficiency due to the reduced number of components.

As a more reliable type of ‘flat’ version clutch, it works well over time however the team needed to find a solution to ensure a smoother system, as the components are less likely to fit together than in alternative setups such as a ‘roof’ dog clutch.

Ahmed comments "We're used to using dog clutches in Formula One, for a racing engine. But it was something completely new for a 'general public' engine. We had to make this simple object usable by customers,"

Cleverly adding a high-voltage starter generator

Ahmed then came up with solution to ensure maximum smoothness by adding a second electric motor, called a High-voltage Starter Generator (HSG). “Its role is to replace the synchronisers of a traditional gearbox to facilitate the clutch and therefore the gear change. By working in conjunction with the electric motor, it allows very precise regulation of the speed of rotation of the gearbox for smooth gear changes."

From this, the original LEGO model concept was updated and tested on the road. It was discovered that the HSG brought other benefits with immediate torque contribution smoothing acceleration at low speeds, avoiding any break in torque delivery when changing gears.

Operating as a series hybrid for enhanced comfort and flexibility, the system did not need an excess of stored energy or a charging socket. Ahmed said: “The possibilities for use in the range were multiplied”, with both E-TECH hybrid and E-TECH plug-in hybrid powertrains now possible.

The teams were reassured of the similarities between the LEGO concept and in simulation also worked ‘extremely well’ in real life.

Find out more about the E-TECH range here